Intel Turbo Boost: On-Demand Overclocking

Intel and AMD continually introduce new CPU technologies, or tweak existing ones, in a global game of one-upmanship. These features are often accompanied by catchy names, but just as often bring little in the way of real-world performance differences. Inventions like Turbo Memory, Application Accelerator, and HD Boost sound cool, but few live up to their advance billing.

But occasionally, a new processor advancement emerges that does yield noticeable improvements in PC productivity. Intel's Hyper-Threading, which lets one CPU core be "seen" as two by compatible software, is an example. When it premiered in Xeon and later Pentium 4 processors, Hyper-Threading was met with some negativity because its resource-splitting virtual processor design was no match for a true dual-core or dual-processor architecture. What critics forgot was that it offered a significantly better multitasking environment than its single-core alternative. More recently, Hyper-Threading resurfaced in the low-power Atom architecture, where it was viewed as a key addition to the netbook segment.

With the flagship Core i7 "Nehalem" release in November 2008, Intel took the intriguing step of not only reintroducing Hyper-Threading, but implementing what the chipmaker calls Turbo Boost technology in a desktop processor line. And last month, Turbo Boost hit the mainstream with the release of Intel's 2010 Core i5 and Core i7 processors.

While Hyper-Threading allows a single core to process two application threads at once, Turbo Boost takes a more old-school approach to performance: Basically, it cranks up the clock speed when software demands and resources allow it.

Turbo Boost 101

Gearheads from the prehistoric days of personal computing will remember the "turbo button," which when pressed would catapult the processor into unheard-of speeds -- from 8 to 10Hz on the old XT. PC gamers and enthusiasts have been overclocking -- running CPUs above their officially rated clock speeds -- for years.

Turbo Boost takes officially sanctioned overclocking to new heights, but by a more sophisticated rather than brute-force route. The technology takes into consideration many different variables, including the number of active cores, program requirements, power consumption, and processor thermals or operating temperatures.

At the top of the speed-limit-setting hierarchy is the number of active cores, and a level below are the CPU temperature, power, and current readings. For example, if a single-threaded application requires more speed, then Turbo Boost will increase the speed of the one core in use. If multiple cores are active, Turbo Boost can still increase clock speeds, though to a lesser extent and assuming that the other factors do not exceed their limits.

This basic process has already been implemented for notebook power savings in the form of technology like Intel SpeedStep, in which an idle processor is down-clocked to baby the battery and reduce thermals. Turbo Mode simply reverses this process: Given the right core usage, power, current, and temperature readings, the CPU will increase clock speed by 133MHz increments until its upper limit is reached.

Newer processors also offer improvements in their Turbo Boost implementation. The first-generation Nehalem CPU only offered a max 266MHz speed jump, while last month's "Lynnfield" models have increased that up to 666MHz. This can be significant, as the 2.8GHz Core i7 860 is limited to its default speed with three or four active cores, but can jump to 3.33GHz with two and to 3.46GHz with only a single core running. No matter the generation, the lower the number of active cores, the higher the potential Turbo Boost will be.

Operating system support naturally includes both Windows 7 and Vista (both 32- and 64-bit), although the Turbo Boost driver is also supported under Windows XP Pro SP3. Knowing that users will be curious about exactly how fast their Core i5/i7 processors are running, Intel has released a Turbo Boost monitoring utility. This Vista Sidebar or Win 7 desktop gadget displays a processor graphic with blue "performance bar" and a readout for default and Turbo Boost clock speeds.